Various proposals have been made in the past to telescopically and automatically operate a car antenna by an operation inside a car. The present applicant has made some proposals in JP,A 279602/1989 (Patent Laid-Open No. 279602 laid open in Japan in 1989), JP,A 206712/1993 and JP,U 52204/1994 (Utility Model Laid Open No. 52204 laid open in Japan in 1994). The inventor of the present invention has made various studies on the production methods of these products and their utilization. In other words, when the automatic telescoping operation of the antenna is carried out in these prior art proposals, a moving operation rotary body, such as a drum or a gear for actuating a wire or a rope for telescoping the antenna element by a worm driven by a motor through a worm wheel, is rotated, thereby telescoping the antenna element. In this instance, the worm wheel is slidably disposed on a support shaft for the worm wheel so that the worm wheel has the function of a limit switch for turning ON and OFF the supply of power to the motor.
According to JP,A 279602/1989, the worm wheel driven by the motor is formed into an intermediate gear portion having integrally formed therewith a small diameter gear portion meshing with a rotary body gear portion. This intermediate gear portion is movably set to a support shaft with a gear support frame having a switch operation portion. A limit switch using a reversing spring is set in each power supply circuit for applying a forward rotation or reverse rotation to the motor, and a flexible arm member is disposed on this limit switch and is operated by the switch operation portion of the gear support frame.
JP,A 206712/1993 describes the following construction. A rotary body for telescoping an antenna element and a worm are rotated through a worm wheel engaging with the worm. An intermediate gear member having integrally formed therewith a small diameter gear meshing the worm wheel with the rotary body is provided, the intermediate gear member being movably fitted to a gear member support frame having an operation portion for a switch disposed in a motor driving circuit. A flexible member for locking is fitted to the gear portion support frame, and an engagement/disengagement mechanism for restricting a torque of movement of the gear portion support frame is disposed between the gear portion support frame and the flexible member for locking. A spherical member and a round fitting hole to which the spherical member is fitted are provided as the engagement/disengagement mechanism.
Further, JP,U 52204/1994 describes the following construction. A fixed contact, a movable contact mating with the fixed contact and a fitting recessed portion for engaging and disengaging a push member are disposed on a movable contact plate as a seesaw type operation member which is pivotally supported at its intermediate portion. A gear holding frame is slidably disposed on a shaft member disposed with a gear on a fixed member. The push member is disposed in a recessed portion formed in the gear holding frame through a spring, and when the gear holding frame slides along the shaft member, the push member is fitted into, and is released from, the fitting recessed portion and turns ON and OFF the movable contact plate with respect to a switch fixed contact.
In the construction of JP,A 279602/1989 described above, a reversing force of the antenna rod operating force is stored in the flexible arm member. Therefore, the antenna can be easily returned to the ON state when the operation is made in the reverse direction, and the antenna operation can be so carried out as to correspond to the ON/OFF operation of the radio receiver. However, this reversing force is so great that the motor is mechanically reversely rotated in some cases, for example. For this reason, there occurs the case where the limit switch is again turned ON and repeats the ON-OFF operation. In other words, the motor output is consumed for the extension or contraction of the antenna during the antenna operation, but under the state where the rotary body stops at the extension/contraction limit or due to an abnormal trouble during the extension operation at an intermediate stage, the propulsion force of the intermediate gear portion increases due to the duration of the rotation of the worm, and the switch operation portion operates the flexible arm member to actuate the reversing movable contact plate of the limit switch, so that the contact is opened and the rotation of the motor is stopped. When the motor stops rotating, the reversing force of the flexible arm member and the resilient reaction of the operation wire generates the reversing operation, and the limit switch again turns ON the circuit by this reversing operation force. Thereafter, the operations in both forward and reverse directions are repeated a great number of times, and the ON-OFF operation described above is repeated. The reversing spring prevents this problem, but there remains the possibility of the repetition of the ON-OFF operation. In this construction, the limit switch becomes complicated in structure and expensive.
JP, A 206712/1993 is directed to solving the problems described above. The first embodiment of this reference uses a reversing auxiliary flexible member corresponding to the flexible arm member of JP,A 279602/1989 as means for obtaining an auxiliary force for returning to the neutral position of the switch, and requires a large number of members besides the slide switch. Therefore, the construction is complicated, there are various conditions for limiting the interaction of these members, and assembly work becomes more difficult. The second embodiment of this reference constitutes the limit switch by a rotary body, and separates the operating force for shifting the rotary body to the OFF state from the operating force for returning to the ON state from this OFF state. A large operating force is necessary for shifting the rotary body to the OFF state as described above, and can be allowed to correspond to the operating force required for the operation of the antenna rod. However, there is no reversing operating force for returning as described above, and the returning operation cannot be attained unless an operating force overcoming the frictional resistance between the members is given.
Namely, when the operating force reaches a set operating force, the UP limit switch is turned OFF and the motor stops rotating, the motor causes mechanical reversing rotation due to the reaction force at that instant, and even when the rod operating force decreases and reaches zero, the UP limit switch cannot be again turned ON. Therefore, there is no possibility of the repetition of the ON-OFF operation, but when the DOWN operation is effected next from this state, there is a reaction force against this operation. If this reaction force is greater than the contact resistance between the members, the antenna element can return and the antenna operation can be carried out in such a manner as to correspond to ON-OFF of the radio receiver. A cam shaped portions having a predetermined cam shape are disposed on both sides of the engagement recessed portion of the rotary body so as to cope with the contact resistance, and these cam shaped portions impart the self-returning force when the reaction force described above is smaller than the contact resistance between the members. However, since this structure is complicated, troubles such as fall-down, unstable rotation, etc., are likely to occur depending on the gap or on the degree of the resistance.
To eliminate the problems described above, it is necessary to apply a grease to the contact surface between the substrate and the rotary body, between the worm wheel support shaft and worm wheel axis and between the worm wheel support shaft and the gear portion support frame, or to restrict the fastening torque of the screw for fitting the rotary body. Further, a rolling body is allowed to disengage at a predetermined operating force and to rotate, and the worm and the support instantaneously move with this disengagement, and their impact sound with the main body case, etc., occurs. Even if a portion such as a rotation stopper is disposed so as to avoid this problem, a similar impact sound occurs at this rotation stopper portion, and such an impact exerts influences on the switch operation and is not desirable. Because a frame body (accommodation hole) for holding the flexible member and the engagement protuberance portion is disposed on the inner wall of the case body, the operation balance of the engagement protuberance with the direct rotary body is lost if any external force acts on the case body or any deformation occurs on the wall surface itself, so that a stable and smooth switching operation mechanism cannot be attained. Incidentally, the rolling body or the engagement protuberance for constituting the engagement/disengagement mechanism in this prior art have a spherical shape, and the engagement portion of the switch rotary body forms a round recessed portion. However, the switching operation between these bodies delicately changes if the lubricating oil and dust adhere to the round recessed portion and to the joint surface of the engagement protuberance, and it has been confirmed that the stable operation cannot always be insured.
In JP,U 52204/1994, further, an operation circuit is formed as a switch whose intermediate state shown in the drawing is just a momentary passing point in any condition and which can be stably held in either side condition. Therefore, when the motor is stopped at the full extension or contraction of the antenna rod or at the overload, the next operation that can be made simultaneously becomes the one that is reverse to the previous operation, and the repetition of ON-OFF does not occur. However, this reference involves the problem that if a radio program is received during the operation of the antenna rod, the antenna does not correspond to the ON-OFF operation of the radio receiver.